Australia's two remaining games are on home soil next week, against England and New Zealand.

While Australia have won three of the four Quad Series so far, Plummer reckons the top tier of the sport is tightening up, mainly through the growing number of international players involved in the powerhouse Australian domestic league.

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The former long-serving Diamonds coach says England's Commonwealth Games triumph, when they pipped Australia 52-51 for gold in April, was symptomatic of gains made by immersion in Super Netball.

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England's best players are spread throughout the league and, increasingly, so are Plummer's leading Proteas.

The Sunshine Coast Lightning defence pairing of South African Karla Pretorius and England's Geva Mentor have been peerless in Super Netball and were at the core of their title defence last month.

Proteas shooter Lenize Potgeiter is among the elite players in the Kiwi domestic league while more of her compatriots are looking beyond the modest South African league.

"You can just see that when they're given an opportunity to go and play in other leagues, they benefit from the harder training and games that are like grand finals every weekend," Plummer told AAP.

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Fifth-ranked South Africa enjoyed their most competitive Quad Series showing in January, when they finished within five goals of victory in all three games.

They were level with Australia entering the dying minutes in London before going down 54-50.

England have retained the bulk of their triumphant Games squad and will be difficult to topple, said Plummer, who is quietly pleased the trans-Tasman monopoly at major tournaments was busted on the Gold Coast in April.

"I'll always want Australia to win, but in the end it was the best thing for netball to have somebody else break the cycle," she said.

"It really had to happen at some stage if the game's going to keep growing."

Plummer also warned New Zealand will bounce back from their miserable fourth-placed Games campaign.

The acquisition of coach Noeline Taurua and return to the court of veterans Laura Langman and Casey Kopua could restore the Silver Ferns to close to their former strength, she said.